<i>B</i>-Allyl-10-Ph-9-borabicyclo[3.3.2]decanes: Strategically Designed for the Asymmetric Allylboration of Ketones
作者:Eda Canales、K. Ganeshwar Prasad、John A. Soderquist
DOI:10.1021/ja053865r
日期:2005.8.24
bicyclic structure. In addition to providing the homoallylic alcohols 6 efficiently (70-92%), the procedure also permits the efficient recovery of the chiral boron moiety (67-82%) as an air-stable crystalline N-methylpseudoephedrine complex 4 for the direct regeneration of 1 with allylmagnesium bromide in ether (98%). The reagent gives predictable stereochemistry, providing a strategically designed "chiral
A highly selective asymmetric domino allylation of aliphatic ketones is described. When methyl ketones 1a-g, the chiral trimethylsilyl ether 2, and allylsilane 3 react in the presence of catalytic amounts of trifluoromethanesulfonic acid, the homoallylic ethers 4a-g are produced with up to 24:1 diastereoselectivity and 89% yield. Cleavage of the obtained tertiary homoallylic ethers C using lithium or sodium in liquid ammonia gives the homoallytic alcohols 5 in 75 to 95% yield and up to 92% ee. Even ethyl methyl ketone 1a, the most difficult example, showed a stereoselectivity of 9:1 at -78 degrees C and 24:1 at -109 degrees C. In addition, the allylation of protected hydroxyalkyl methyl ketones 7a-j was investigated to give the corresponding homoallylic ethers 8a-j with a diastereoselectivity of up to >24:1 and 98% yield. In contrast, ethyl alkyl ketones 1h-j have a low selectivity.
Facial-Selective Allylation of Methyl Ketones for the Asymmetric Synthesis of Tertiary Homoallylic Ethers
作者:Lutz F. Tietze、Sören Hölsken、Jens Adrio、Tom Kinzel、Christoph Wegner
DOI:10.1055/s-2004-829153
日期:——
The stereoselective allylation of methyl ketones is described to give tertiary homoallylic ethers, which can easily be transformed into homoallylic alcohols by a Birch reduction. Reaction of methyl ketones 4 with allylsilane 5 in the presence of the chiral TMS ether 3a and a catalytic amount of trifluoromethanesulfonic acid led to homoallylic ethers 6 in high yield with a selectivity of 9:1 to >20:1